1. Field of the Invention
The present invention is in the field of one-way valves designed to replace diseased venous or arterial valves present in the circulatory system. More specifically, the present invention is directed to the replacement of the aortic, pulmonary, or peripheral vein valves. The present invention is also directed to a holder that maintains the valve's geometry during its surgical implantation and assists the surgeon to orient it correctly.
2. Description of Background Art
The Sigmoid Valves
The mammalian circulation needs the presence of one-way valves to maintain forward blood flow. These valves are found in the outflow of the right and left ventricles (“pulmonary” and “aortic” valves, respectively) and in the large veins. Because of their similar anatomic structure, they are called “sigmoid” or “semilunar” valves. This common structure consists of one, two, or three very thin flaps called “cusps” or “leaflets.” Each flap has a semicircular shape with a curved free edge and a curved base that is inserted into the vessel wall. The insertion of the free edge of the cusp to the vessel wall is called the “commissure.” Immediately downstream to each leaflet, the wall of the vessel has a dilatation or bulge called the “sinus of Valsalva.” There are as many sinuses of Valsalva as leaflets; a trileaflet valve has three sinuses. Historically, the sigmoid valves were understood to be formed only by these leaflets. Recent studies by the present inventor and colleagues have shown however that the aortic valve (as a model of all sigmoid valves) must include two or three leaflets; their crown-shaped base of attachment to the vessel wall known to cardiac surgeons as the “valve annulus;” the sinuses of Valsalva, the sinotubular junction or supra-aortic crests that delineate the upper limit of each sinus of Valsalva, and in the case of the aortic valve, the origin of the two coronary arteries or “coronary ostia.”
The nature of dynamic changes that occur in the geometry of the aortic and pulmonary valves during the cardiac cycle was also studied recently by the present inventor and colleagues using ultrasound crystals to provide data. Three-dimensional reconstructions were obtained at 200 frames per second. These newly acquired anatomic and physiologic data have a very significant impact on the design of new sigmoid prostheses and constitute the scientific basis for the present invention.
Sigmoid Valve Replacement
In disease, the function of the sigmoid valves is impaired either through narrowing of the valve (“stenosis”) or lack of complete closure, which results in backflow (“regurgitation”). In both circumstances, the whole circulation of the blood and of the heart is altered giving rise to severe symptoms in the patient.
Cardiac sigmoid valve replacement with prosthesis is a tribute to the imagination of cardiac surgeons and engineers. After open-heart surgery became available, parallel development of mechanical and tissue valves continued. Further description here concentrates only on tissue valves, because only these are truly relevant as background to the present invention. In the decade of the 1960s, there was an explosion of new tissue valves. At Oxford University, England, a surgical method was developed to dissect, prepare, and implant a human cadaver aortic valve in its anatomic (i.e., subcoronary) position (see Duran et al.: A method for placing a total aortic homograft into the subcoronary position. Lancet 1962;2:488–489). This technique was applied for the first time in 1962 (see Ross: Homograft replacement of the aortic valve. Lancet 1962;2:487). It consisted of removing as much non-valvular tissue as possible so that only the three leaflets were sutured to the patient. This was the origin of the use of homografts that even today remain the preferred valve replacement alternative because the patient does not need permanent anticoagulation therapy. This operation was improved by Barrat-Boyes, who placed the aortic homograft with a double suture line (see Barrat-Boyes et al.: Long-term follow-up on patients with the antibiotic sterilized aortic homograft valve inserted free hand in the aortic position. Circulation 1987;75:768–772). The homograft was dissected in a more tubular fashion, and was held in position by a proximal suture line that anchored the inflow orifice of the homograft to the outflow of the ventricle and a distal suture line that joined the homograft aortic wall to the aortic wall of the patient. This technique has become the preferred method for the surgical implantation of all aortic homografts and stentless bioprostheses.
Because of the difficulty of obtaining cadaver valves, the art also developed an interest in using porcine valves. In 1965, the first aortic xenograft (porcine) clinical implant was performed (see Binet et al.: Heterologous Aortic Valve Transplantation. Lancet 1965;2:1275–1277). The technical difficulty of correctly implanting these stentless valves gave rise to the idea of mounting the porcine valves into a frame or stent made of metal or plastic covered with DACRON™ cloth. These stented xenogeneic valves are called “bioprostheses,” and presently constitute approximately 40% of all heart valve replacements.
More recently, awareness of the limitations of the mounted, stented bioprostheses has rekindled the interest in the “stentless bioprosthesis,” where chemically treated porcine aortic valves are supplied as a complete aortic root that can be used as a complete root replacement or can be cut down to fit within the aortic root of the patient using the Barrat-Boyes technique (see David et al.: Aortic Valve Replacement with Stentless Porcine Aortic Valve Bioprosthesis. J Thorac Cardiovasc Surg 1990;99:113–118). The surgical techniques of implanting such stentless valves are far more demanding than when a standard stented valve is used. The main technical difficulties are due to the floppiness of the valve, resulting in a defective implantation, and in the case of the aortic valve, interference with the coronary ostia. These difficulties have significantly limited the use of stentless valves.
A different surgical alternative is valve repair. Because of the long-standing interest in mitral valve repair, the art tried to expand the field of repair to the aortic valve. It soon became apparent that the main problem, different from the mitral valve, was the lack of sufficient valve tissue to achieve competence. As a solution, the pericardium of the patient was selected to extend the aortic leaflets. In this technique, the pericardium is fixed and trimmed using specially designed molds (see U.S. Pat. Nos. 6,352,708 and 6,491,511). Sixty-five patients underwent this procedure and are being followed for a maximum of 12 years with satisfactory results. In the course of developing the present invention, a series of in vitro and in vivo experiments were conducted. These experiments led to the present invention, which renders the surgical implantation technique of using pericardium or like membrane in valve replacement significantly less difficult.